1. Field of the Invention
The present invention relates to an optical apparatus such as a digital camera, a video camera, or an interchangeable lens, and more particularly to an optical apparatus having a mechanism that guides a lens holding member by a ball in an optical axis direction.
2. Description of the Related Art
As a guide mechanism which guides a lens holding member holding a lens so as to be movable in an optical axis direction, a mechanism in which a guide bar extending in the optical axis direction is used is often adopted. However, in a guide mechanism in which a guide bar is used, because there is necessarily a minor backlash between the lens holding member and the guide bar, a displacement is generated by the backlash in a plane orthogonal to the optical axis of the lens holding member (i.e. lens). Therefore, the optical performance of the optical apparatus is degraded.
As a countermeasure against reducing such a backlash between the lens holding frame and the guide bar, it is considered that a biasing mechanism having a biasing force for pressing the lens holding frame with respect to the guide bar is provided. However, when biasing force acts, the drive load of the lens holding frame increases in accordance with the increase of the frictional force between the lens holding frame and the guide bar.
Japanese Patent Laid-Open No. 05-034556 discloses a lens barrel in which a plurality of balls held by a retainer are arranged between a fixed barrel and a lens holding frame, and the ball performs a rolling motion in a V-shaped groove section provided on the lens holding frame in accordance with the movement of the lens holding frame with respect to the fixed barrel in an optical axis direction. In the lens barrel, a biasing mechanism where balls are arranged at three areas in a circumferential direction and one of the balls is pressed to the V-shaped groove section by a spring force and the other two balls are pressed to the fixed barrel by the lens holding frame receiving the pressing force is adopted. According to the configuration, a minor backlash of a lens holding frame with respect to the fixed barrel is eliminated and a small sliding friction is only generated between the lens holding frame and the fixed barrel by the rolling motion of the ball to suppress the increase of the drive load of the lens holding frame.
However, in the configuration disclosed in Japanese Patent Laid-Open No. 05-034556, the rotation of the lens holding frame with respect to the fixed barrel in a direction around an optical axis is prevented by engaging a pin provided on the lens holding frame with a key groove section formed on the fixed barrel. In other words, the guide of the lens holding frame with respect to the fixed barrel in an optical axis direction is performed by the engagement of the pin and the key groove section. A sliding friction greater than a rolling friction is generated between the pin and the key groove section. Therefore, the drive load of the lens holding frame increases.